This invention relates generally to a heat and pressure fusing apparatus and, more particularly, to imaging media removal apparatus for separating imaging media such as plain paper from a heated fuser roll.
In a typical electrophotographic copying or printing process, a charge retentive surface such as a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is selectively exposed to light to dissipate the charges thereon in areas subjected to the light. This records an electrostatic latent image on the photoconductive member. After the electrostatic latent image is recorded on the photoconductive member, the electrostatic latent image is rendered visible by bringing one or more developer materials into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules either to a donor roll or to a latent electrostatic image on the photoconductive member. When attracted to a donor roll the toner particles are subsequently deposited on the latent electrostatic images. The toner powder image is then transferred from the photoconductive member to a final substrate or imaging media. The toner particles forming the toner powder images are then subjected to a combination of heat and/or pressure to permanently affix the powder images to the copy substrate.
In order to fix permanently or fuse the toner material onto a substrate or support member such as plain paper by heat, it is necessary to elevate the temperature of the toner material to a point at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow to some extent onto the fibers and/or into the pores of the support member or otherwise upon the surface thereof. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be bonded firmly to the support member.
One approach to thermal fusing of toner material images onto the final substrate or imaging media has been to pass the substrate with the unfused toner images thereon between a pair of opposed roller members, at least one of which is internally heated. During operation of a fusing system of this type, the substrate to which the toner images are electrostatically adhered is moved through a nip formed between the pressure engaged rolls with the toner images contacting the heated fuser roll to thereby effect heating of the toner images within the nip.
A plurality of stripper fingers is usually provided for effecting separation of the final substrate or imaging media from the heated fuser roll. The fingers physically contact the surface of the heated fuser roll such that the tips thereof are inserted between the lead edge of the imaging media and the heated fuser roll. Stationary baffles have been employed for receiving the imaging media once it has been separated from a heated fuser roll. Such baffles are supported in a fixed position downstream of the fuser nip for transporting or guiding imaged substrates toward the exit of a reproduction machine.
Contact stripper fingers typically leave disruptions in the toner on an imaging media or substrate such as plain paper, often severe enough to be objectionable to the customer. To obviate the foregoing problem, Nip Forming Fuser Rolls (NFFR) and/or air stripper systems have been utilized for separating or stripping of imaging media from the heated fuser roll. The air stripper approach works well in eliminating finger marks but the cost of an air stripping system is quite high and consumes 300-500 additional watts for the compressor and is a fairly complex arrangement. Thus, in order to avoid the higher cost and complexity of air stripper devices, improvements in contact stripping of substrates are most desirable.
Accordingly, the present invention is directed to an improved image media removal apparatus for separating imaging media such as plain paper from a heated fuser roll. To this end, there is provided a stripper finger structure movable between standby and active positions for separating the lead edge of the imaging media when in its active position and a stripper baffle structure movable between standby and active positions for separating the imaging media beyond the lead edge thereof.
Following is a discussion of references, the disclosures each of which are lo hereby incorporated by reference in their entirety.
U.S. Pat. No. 3,578,859 granted to William K. Stillings on May 18, 1971 discloses apparatus to remove an insulating copy sheet from a moving photoconductive surface, the copy sheet being electrostatically tacked to the surface prior to removal by a corona discharge device during a xerographic image transfer operation. A stripping finger is arranged to lift the leading edge of a sheet being advanced on the photoconductive surface and to direct the sheet upwardly away from the surface. A stationary transport having a smooth flat platen to receive a stripped copy sheet in sliding relation therewith is positioned to intercept the leading edge of the stripped sheet and direct the sheet towards a subsequent processing station. Suction ports in the platen located behind the point of contact of the leading edge of the sheet lift the body of the sheet from the stripper finger and hold the sheet in sliding contact with the platen. Lifting means raise the stripper finger away from the moving surface and further stripping of the sheet is accomplished as the sheet slides along the platen and is lifted from the drum surface.
U.S. Pat. No. 3,844,252 discloses a sheet removal device for separating an image bearing support sheet from the surface of a heated fuser roll. The removal device is constructed in a configuration and of a material to prevent copy degradation and harming of the fuser roll during the sheet separating operation.
U.S. Pat. No. 4,065,120 granted to Fromm et al on Oct. 13, 1998 discloses a slidably and pivotally mounted means for stripping copy paper from one or both rolls of a fuser assembly in a photocopying machine. Spring means urging the stripping means into contact with a roll is normally countered by a component of frictional force exerted by the roll on the stripping means, thereby avoiding exertion of undue pressure on the roll. If copy paper becomes adhered to and cannot be detached in a normal manner from the roll, the stripping means is moved to a position in which the tip portion thereof no longer contacts the roll, thereby avoiding damage to the roll and stripping means.
U.S. Pat. No. 4,028,050 granted to Ari Bar on Jun. 7, 1977 discloses apparatus where stripping copy sheets from a heated fuser member utilized in a xerographic copier. The apparatus is characterized by the provision of a plurality of stripper fingers and combination support and bias means therefor wherein the support and bias means comprises a unitary member and each stripper finger in conjunction with its associated unitary member constitutes an integral assembly. The assemblies are fixedly supported adjacent the fuser member whereby the leading edges of the stripper fingers engage the fuser member to strip the copy sheets therefrom. The position of the assemblies can be varied in order to vary the pressure exerted by the stripper finger on the fuser assembly.
U.S. Pat. No. 4,119,307 granted to Ralph A. Hamaker on Oct. 10, 1978 discloses an apparatus in which a stripping member separates a sheet adhering to a moving member. The stripping member is translatable so as to maintain the spacing between the moving member and the surface of the stripping member opposed therefrom substantially constant.
U.S. Pat. No. 5,406,363 granted to Siegel et al on Apr. 11, 1995 discloses an apparatus for minimizing fuser misstrips from a heat and pressure fuser in an electrophotographic printing machine. A plurality of sensors are provided to determine the basis weight of the copy sheet, the density of the image being transferred to the copy sheet and fused thereon, the relative humidity of the machine environment, the process speed of the print engine, etc. Signals indicative of all the variables are generated and sent to the machine controller, which processes these signals and predicts when a fuser misstrip is likely to occur. Based on the likely degree of misstrip, a variety of actions are taken to prevent the misstrip. A stripper finger can be actuated to physically remove the sheet from the fuser member and/or the release agent management system can vary the amount of release agent applied to the fuser to assist in the removal of the copy sheet from the heated fuser member. The overall system provides the advantage of a varying amount of fuser release agent so that an extreme buildup of oil is not encountered, and further allows an intermittent stripper finger use to prevent premature wear of the fuser member by the constant pressure of a stripper finger.
U.S. Pat. No. 5,623,720 granted to Howe et al on Apr. 22, 1997 discloses a novel method and apparatus for rotating a stripper bar associated with a paper path. A cam and cable mechanism replaces a rigid link mechanism on the stripper bar, the cam and cable mechanism providing for a much greater angle of rotation of the stripper bar than the rigid link mechanism. The additional rotation allows the stripper fingers on the stripper bar to be rotated completely out of the way of a paper jam clearance path. Other new developments include a wrench positioning system that controls the orientation of the stripper bar and an over- rotation prevention system that stops the rotation of the stripper bar when the stripper bar and stripper fingers are being serviced.
The present invention provides an imaging media removal apparatus including a stripper finger structure for separating the lead edge of the imaging media and a stripper baffle structure for effecting separation of the imaging media beyond the lead edge. The stripper fingers are active for the first 3-15 mm of the imaging media after which imaging media stripping is under the control of the stripper baffle structure which is moved into close proximity to the nip exit of the fuser for that purpose.
The stripper fingers operate intermittently, that is, they are activated from a standby position as a group, prior to the imaging media arriving at the fuser nip exit, during the inter copy gap, and remain functional until the media is under the control of a stripping baffle, approximately 2-75 mm, preferably 3-15 mm after the lead edge of the imaging media has moved past the stripper finger tips. Unlike prior art baffles; the exit baffle of the present invention is moved to a position in close proximity to the fuser roll within 0.5-1 mm away. The prime benefit of the invention is that stripper finger marks are limited to the first few millimeters of the media when there is development material in that area and a secondary advantage is that the finger tip wear would be reduced because of the reduced time the fingers are actively stripping. The movement of the baffle into close proximity of the strippers allows the stripper fingers to function for a shorter time interval as compared to prior art devices. In other words, the fingers remain in contact with the imaging media for only a short interval of time.